Can someone explain to me how a larger area of autofocus is a good thing. How does the camera know where in the frame you want the focus, surely spot focus is going to be more accurate??

The first AF cameras had a single AF point in the middle of the frame. Later cameras came with modules that had more AF points. The First mirrorless cameras from Sony with PDAF had the PDAF AF points grouped in the centre of the frame. The A6000 has them in about 90% of the frame, it is not one big AF point but there are 179 AF points. When tracking a subject that moves in the frame, the AF sysem can follow that subject by using the tight AF point(s) The system can in the end predict where the subject will be in the next frame and prepare focus for that frame...